We propose to continue efforts to establish the presence of several hydroxycholesterol derivatives in human blood and to develop microanalytical assay methods for the sterols, thereby to apply the assay methods to selected human plasma samples in an effort to correlate health status with sterol levels in patients. Our analytical methods will include high pressure liquid column chromatography and combined gas chromatography-mass spectrometry, using either or both electron impact ionization and chemical ionization. We also plan to use capillary column gas chromatography as a new aspect of our work. The sterols to be sought are 26-hydroxycholesterol, 24-hydroxycholesterol, and 25-hydroxycholesterol.